In the pursuit of ever higher efficiencies, gas turbine manufacturers have long relied on higher turbine inlet temperatures to provide boosts to overall engine performance. In typical modern engine applications the gas path temperatures within the turbine exceed the melting point of the component constituent materials. As such, conventional configurations extract dedicated cooling air from the compressor to cool gas path components in the turbine incurring significant cycle penalties especially when cooling is utilized in the low pressure turbine (sometimes also referred to as the power turbine).
The amount of cooling air needed over the mission of the aircraft is typically calculated and sized based off a single worst-case operating point. The severity of this operating point is further exacerbated by assuming that the over-all engine performance is based on a low probability stack up engine (typically referred to as a 2 sigma engine) at the end of the engine's service interval. Though this ensures adequate part durability performance over the life of the engine, it creates an over-arching performance drain.
A number of technologies exist that attempt to modulate the cooling flow to the turbine. These range from passive temperature driven systems that modulate the flow to a specific component to active system-style modulation devices. Some modulated cooling methods integrate active measurement of engine parameters such that at different exit compressor pressures and turbine exhaust temperature (or other parameters), the cooling may be modulated according to the predisposed working of the engine.
The blade exterior temperature can also be estimated based on measured cycle conditions and analysis-based constant cooling effectiveness and the coolant system modulated as a function of estimated blade thermal loading. This method in estimating turbine blade metal temperatures via mission parameters and constant cooling effectiveness as defined by:phi=(Tgas−Tmetal)/(Tgas−Tcool)This method has several shortfalls in that constant cooling effectiveness, especially with the implementation of thermal barrier coating (TBC), does not track linearly with blade heat loading.
It is commonly known that the effectiveness of TBC decreases in reducing over-all blade surface temperatures as the external heat loading parameters (such as external gas temperature or heat transfer coefficient) decrease.
There is a desire to determine real-time radially resolved temperature measurements from a turbine blade to be utilized in engine controls and operations.